For many decades, the clinical significance of prolonged duration of action for drugs used in the control of heart disease has been appreciated. It is recognized that many life-threatening heart disorders occur in recurrent episodes. This pattern is typified by the attacks of angina pectoris (chest pain) and especially disorders of heart rhythm such as ventricular arrhythmias and in particular atrial fibrillation. Indeed, arrhythmia currently is the most common serious disorder of the heartbeat. It is responsible for much morbidity as well as mortality. Thus, drug therapies targeting these conditions require continuous drug action without periodic or intermittent lapses due to suboptimal drug concentrations between dosing intervals. There remains a need for better drug formulations to control heart disorders.